1. Field of the Invention
The present invention relates to methods of dispersing cyclodextrins into polyolefins and to the products made from polyolefins containing cyclodextrins dispersed by this method.
2. Background Art
Cyclodextrins are cyclic, polymeric sugars which have a truncated conical shape and a hollow interior. The interior cavity is relatively hydrophobic compared to the hydrophilic exterior which bears many hydroxyl groups. The size of the cavity depends upon the number of glucose units (typically ranging from 6 to 12 units) in the cyclodextrin ring. Diameters vary from about 5 Å for α-cyclodextrin (6 glucose units) up to about 8 Å for γ-cyclodextrin (8glucose units). Correspondingly, the interior volumes range from about 170 Å3 to about 430 Å3. A significant amount of low molecular weight material can occupy the cavity. Cyclodextrins typically form inclusion complexes with 1:1 or 1:2 stoichiometry depending upon the low molecular weight substrate. They are useful as adsorbents for odors, flavors, dyes, etc., as well as being useful as carriers for material such as perfumes, fabric softeners, antibiotics, dyes, inks, etc.
There has been significant interest in putting cyclodextrins into or onto polymeric materials for such varied applications as removing odors from inanimate surfaces, adsorbing undesirable flavor components, and improving polymer barrier properties. (See, for example, U.S. Pat. Nos. 5,776,842, 5,837,339, 5,882,565, 5,883,161, 5,928,745, 5,985,772, 6,136,354, 6,218,013 and 6,306,936.) The mechanism by which cyclodextrins improve the barrier properties of polymers involves non-steady state diffusion. Cyclodextrins reversibly adsorb a permeant when it begins to penetrate a polymer film. As the permeant adsorbs and desorbs in the cyclodextrins, the apparent permeant concentration is temporarily higher than it would be at steady state. Such non-steady state behavior slows the permeation rate making it appear that the film has improved barrier properties. While this example illustrates the ability of cyclodextrins to capture small molecules, there are other examples in which cyclodextrins in a polymeric matrix deliver small molecular species. For example, there are fibers that release anti-microbials, fabrics that release fabric softeners while in a dryer, and films that release perfumes to mask odors.
Cyclodextrins are difficult to disperse in polyolefins because typically cyclodextrins are powders with hydrophilic surfaces. In particular, cyclodextrins tend to agglomerate without any surface treatment. Such agglomeration has a deleterious effect on the mechanical properties of the polymer and also reduces the effectiveness of the cyclodextrin to function as an adsorbent or carrier.
Recently, cyclodextrins have been grafted onto polypropylene modified by electron-beam grafting of glycidyl methacrylate (“GMA”). The cyclodextrin is grafted when hydroxyls on its surface react with the epoxides of the grafted GMA (J. Appl. Polym. Sci. (2000), 77(10), 2118–2125). However, electron-beam modification is not a feasible process for commercial production of cyclodextrin derivatized polypropylene because of the expense associated with this process.
Accordingly, there exists a need for improved methods of dispersing cyclodextrins in polymers, and, in particular, into hydrophobic polymers such as polyolefins.